(1) Field of the Invention
The present invention relates to a packaging container for acrylamide crystals and a packaging method for acrylamide crystals. More particularly, the present invention relates to a packaging container and a packaging method for preventing condensation of moisture contained in the crystals on the inside surface of an inner bag when the temperature is changed in transportation or storage.
(2) Description of the Related Art
Acrylamide can be prepared by a process for catalytically hydrating acrylonitrile in the presence of a catalyst containing metallic copper as a primary component or by a process for hydrating acrylonitrile through the action of microorganisms Acrylamide is a very useful compound which is widely used as a raw material for polyacrylamide having many applications such as flocculant, paper reinforcing agent and petroleum salvaging agent.
Acrylamide is produced in the form of an aqueous solution, and usually transported or stored as a 30 to 50% aqueous solution. It is also used for polymerization reaction in the form of an aqueous solution.
However, crystallized acrylamide is required in the case of transporting over a long distance, storage in a cold district or use in a non-aqueous system.
Crystallized acrylamide is precipitated by concentrating and cooling the aqueous acrylamide solution and obtained by successively filtering and drying.
The crystallized acrylamide thus obtained is usually packed in a multi-ply paper bag composed of one plastic layer such as polyethylene, polypropylene and vinylidene chloride and 3 to 5 layers of kraft paper, and transported or stored.
In order to correspond to a specific application where contamination of foreign substances must be carefully prevented, a packaging obtained by using a double-ply inner bag such as polyethylene bag or polypropylene bag is placed in a pail can, completely sealed, and further packaged in a corrugated box and is transported or stored.
However, the crystallized acrylamide thus obtained often leads to some trouble that moisture contained in the crystal condenses on the inside surface of the inner bag in transportation or storage. In packing powder or crystals, a packaging method which maintains its dry state by using a moisture-proof packaging material and a drying agent for packaging, is generally employed in order to protect the package content from outside moisture. In such case, the content to be packaged is sufficiently dried prior to packing.
In packaging the crystallized acrylamide, moisture contained in the crystals is condensed on the inside surface of the inner bag in transportation and storage and hence the above packaging method cannot solve the problem of moisture condensation. By directly adding a package of drying agent such as silica gel into the inner bag containing acrylamide crystal, the moisture condensation on the inside surface of the inner bag can be generally prevented. However, a packing bag of the drying agent can be broken by mechanical friction with acrylamide crystals during transportation and causes troubles. For example, when the acrylamide crystals around the drying agent are examined by dissolving the crystals in water, lint like foreign particles are found. Such particles lead to problems in use. In other cases, the drying agent and acrylamide crystals are mixed in the packaging bag and extremely complicated procedures are required for selectively picking out the drying agent.
On the other hand, in the steps of concentrating, cooling and precipitating the aqueous acrylamide solution and filtering and drying the crystallized acrylamide, the resulting crystals are pulverized in the course of reducing the moisture content of the crystal as low as possible. Thus, problems on safety and health result from the dust generated. Even though the moisture content of the crystal is reduced from the usual range of 0.5 to 1.0 wt. % to the range of 0.2 to 0.5%, moisture condensation still occurs after packaging.